The present invention relates to a kimchi fermentor, and particularly to a kimchi fermentor and control system thereof using a kimchi curing sensor.
Kimchi is made of pickled vegetables including radish, cabbage and cucumber, and it is an indispensable dish in Korean cuisine. However there have been numerous problems in its mass production and mass storage until now, because kimchi is a naturally fermented food and fermented kimchi has the defect of acidifying itself at room temperature.
Due to these problems, it is difficult to properly cure and produce kimchi on a commercial scale. While the problem of preserving cured kimchi for long periods is well known, it can not be said that the unique taste of kimchi is truly preserved without controlling the fermentation for its curing. For example, with respect to the spread of refrigerator services for preserving kimchi, refrigerators have been used predominantly for preserving kimchi for long periods. But kimchi stored in refrigerators ferments even at relatively low temperatures. Also, kimchi produces a unique odor which greatly influences other foodstuffs stored with it. Therefore, kimchi has not been produced to have the right taste in a refrigerator.
In light of this, it is an innovation if kimchi can be easily prepared to have the right taste, and the right taste can be preserved for a long time. Therefore, it is desirable that kimchi have its degree of curing determined by means of a sensor, which can detect and measure the degree of curing based on physiology, and that kimchi can be stored while maintaining the right taste for a long period. Conventional methods for automatically preparing kimchi however, comprise only the steps of pickling kimchi, then controlling the fermentation period and temperature. Thus, undesirable results have been caused by the kimchi manufacturing process, the fermentation period and temperature, or the type of spice and the quantity of sauce. That is to say, kimchi is a product with a sour taste, due to the organic acid obtained when microorganisms increase in the pickled vegetable and the fermentation phenomenon occurs during kimchi curing. It is well known that the taste of kimchi is greatly influenced by the type of vegetable used, the type of the organism associated with kimchi, the salt concentration, and the temperature acting decisively to the increase of the number of microorganisms.
Therefore the design and construction of a kimchi fermentor must consider the fermentation physiology of kimchi. Also it has been an important task, in order to automatically manage the curing of kimchi, that optimum control variables be derived which correspond to the degree of curing. Previously, the kimchi fermentation characteristics reported in Korea and overseas are its acidity, or pH level. Thus the present invention aims at the design and construction of a kimchi fermentor, which uses the change in acidity pH as the measuring variables. However, installing acidity measuring equipment in a home refrigerator would be very expensive and not economical. Furthermore, even if an acidity sensor were used in a refrigerator, a standard buffer solution must be used which could contaminate the kimchi. Also, if the acidity electrode were accidentally broken, the mercury and silver which are the constituent parts could cause serious contamination. Therefore, it is very important that new variables be found which are capable of indicating kimchi curing. Furthermore the variable adapted to the automatic control of a kimchi fermentor must be easily convertible into a reliable electric signal. Thus, it is further desirable for a kimchi fermentor to have a variable which is economical to measure and provides a stable electric signal.
In order to find a variable adapted to kimchi curing, pressure changes relative to kimchi juice and the amount of gas produced during fermentation have been measured. That is, the representative physical change after preparing kimchi is to produce kimchi juice. Therefore it is known that changes in the amount of kimchi juice are easily measured and also are easily converted into electric signals. It has been proven, however, that the change in the amount of juice is caused by the protoplasm separation phenomenon and is in equilibrium sooner, whereas the amount of kimchi juice formed under various artificial temperatures and conditions have not for the most part been influenced by the degree of temperature. Thus, it is well known that the change in the amount of juice cannot be used as a variable representing the beginning of kimchi curing or of the fermenting status.
In connection with the amount of the gas generated while fermenting kimchi, it has been published that kimchi curing is closely related to the activities of microorganisms but is independent of acidity. Substantial kimchi fermentation mechanism makes the group of the anaerobic or facultative microorganism, including Lactobacillus plantarum, which dissimilate the vegetables directly or the microorganism increases in the basic dissoluable filtered solution to produce organic acid and CO.sub.2. At that time, the concentration of the organic acid represents the acidity, which had been broadly used as the index of kimchi curing. Thus it is found that if a method is developed for effectively measuring the amount of a gas produced, such as CO.sub.2, it has the high possibility of practical application as an index of kimchi curing, much the same as the acidity value commonly used. Specifically, gas measurement is more easily performed than acidity measurement, and the cost for constructing gas measuring apparatus is low.
Accordingly, a pressure cell was used to measure the amount of gas produced by fermenting kimchi, in which a kimchi sample was put in the pressure cell and then the pressure cell inserted into a case having kimchi to be fermented. Herein it is noted that the pressure cell has a capillary tube connected to a transducer, which measures the pressure and converts the pressure into an electrical signal. Therefore the pressure produced in the pressure cell was measured through the capillary tube at the transducer. As a result, it was experimentally confirmed that the pressure in the cell represented a curve similar to that of the microorganism increase, but after the lapse of 24 hours time the pressure in the cell had not further changed. During this experiment, kimchi had its acidic taste when the pressure in the cell was at the highest level. Its taste was equal to that of kimchi when the CO.sub.2 gas is produced in the largest quantity.
Therefore it has been proven that a pressure cell can be used as the sensor for measuring kimchi curing, but the reproducabilty of the measurement must be proven in order for it to be useful as sensor. As to it, it had been observed whether the amount of kimchi sampled from the prepared kimchi is fermented in the sensor cell and which prepared kimchi is put in a kimchi case along with the sensor cell. As a result, it has been found that since the fermentation of kimchi is not relative to true cultivation but to natural increasement, the growth aspects of the bacterium differ between kimchi in a case and kimchi samples in the kimchi sensor was developed in accordance with the lapse of the fermenting time even though the same samples were used at the time being intended to prepare kimchi. That is, because the growth environment of the bacterium in the pressure cell is different from the growth environment of the bacterium in the kimchi case, the possibility for inhibiting the growth was overlooked. Thus the pressure cell does not have the same reproducability as the sensor for sensing kimchi curing.
In the procedures of these studies, it has been found that kimchi induces generation of gas during fermentation. The gas generated as the product of the basic disassimilating metabolism and the respiration of the microorganism is dissolved in part in the kimchi solution but is mostly discharged out of the kimchi solution forming a gas bubble. It has been observed that the generation of gas bubbles usually does not occur at the beginning of fermentation, when the concentration of the bacterium is relatively lower. Upon reaching the logarithmic growth phase, however, gas bubbles are significantly increased in size and number and become capable of being seen with the naked eye. The present invention requires apparatus which can collect the gas in an open kimchi case, in order to overcome the disadvantages causing the failure of the control system due to air exposure of the kimchi case due to less than perfect sealing of the pressure cell.
Considering these points, it should be noted that the sensor for sensing kimchi curing may have variables according to the kimchi preparing, if the sensor has the reproducability and senses the curing degree of kimchi under various temperatures and conditions. Thus if this kimchi curing sensor is developed, a kimchi fermentor is easily constructed. Also a kimchi fermentor must be easily controllable on the basis of the variables obtained from the kimchi curing sensor. Since the kimchi fermentor is designed or configured on the basis of the fermenting process, the fermenting procedure must be accurately measured, and kimchi fermenting status and environment must be controlled before executing the design of the refrigerator. Also the design of a kimchi fermentor must consider the growth characteristics of the microorganism, including physiological characteristics, and the mechanical and electronic characteristics of the control system, as a single system. For example, it takes about one week to complete the procedures comprising the steps of pickling kimchi and curing it through fermentation. Further kimchi fermentation must be accompanied through reiterated experiments because it is not a true cultivation which has its properly configured method relative to the automatic fermenting system of kimchi. Therefore the fermenting control system of kimchi must comprise all parts substantially required for the design of a kimchi fermentor as well as the measuring and controlling systems.